Wood Protection Bulletin Western Division Canada’s National Wood Products Research Institute July 2003 Properties of Lumber with Beetle-Transmitted Bluestain Users of lumber are probably familiar with bluestain. Some may wonder if the amount and type of stain transmitted by the mountain pine beetle affects the wood in any way. Compre- hensive testing recently confirmed that beetle-transmitted bluestain has no practical effect on strength properties or gluing characteristics. Neither does the bluestain affect the adhe- sion of furniture finishes. The stain causes some possibly beneficial changes to dimensional stability, checking and permeability. R egular customers for western spruce-pine-fir lumber have probably seen some bluestain, a subtle streaking in the lumber. At the moment, bluestain is more prevalent than in the past, because British Columbia is currently experiencing a large natural outbreak of mountain pine beetle (MPB). Native to the forests of western North America, the MPB attacks several species of pine trees, including ones commonly used for construction lumber and panels. The beetle carries with it a staining fungus that weakens the tree’s defences which allows the insect to lay eggs under the bark. While the beetle stays just under the bark, the fungus can grow throughout the sapwood (the outer part of the tree) feeding on sugars, carbohydrates and other nutrients contained within the wood cells. As the fungus spreads, it leaves behind a permanent blue or grey stain that colours products made from this wood. Neither the beetle nor the fungus eats the wood structure itself. Bluestain fungi are not mold, nor do they cause decay (rot) problems. They are considered harm- less with respect to both wood products and peo- ple, and are typically dead by the time the wood products leave the manufacturer. The wood can be handled exactly as with non-bluestained wood. Because it looks slightly different, questions are sometimes asked about bluestained wood. Forintek performed a series of tests to address any possible marketplace concerns and to provide a scientific basis for the anecdotal evidence that bluestained wood is equivalent to non- bluestained wood. Eastern Division Western Division 319, rue Franquet, Sainte-Foy, QC G1P 4R4 2665 East Mall, Vancouver, BC V6T 1W5 Tel: (418) 659-2647 Tel: (604) 224-3221 Fax: (418) 659-2922 Fax: (604) 222-5690 www.forintek.ca Property Tested Results Implications Stiffness and No significant difference. These are the most important strength breaking strength properties for structural applications. Bluestained wood is as strong and as stiff as non-bluestained wood. Impact resistance Slightly lower (5%) impact Toughness is not a critical strength (toughness) resistance for bluestain. property for most end-uses of wood but is one of the first properties affected by biological agents. The small reduction is much lower than previously reported for other types of wood and staining fungi and is of no practical significance in construction. Truss plate grip Measurable (6%) increase in Good plate grip capacity is critical for the capacity ultimate grip capacity but similar design and manufacture of trusses. The slip for bluestained wood as for non- measured increase is not of practical stained wood. significance for truss design. Dimensional Bluestained wood was significantly Bluestained wood seems to develop stability and less prone to warping when tested in micro-checks (hairline cracks). This may checking (in our simulation of outdoor exposure. have implications for kiln-drying practices, as repeated wetting/ Cracks were significantly smaller in well as potential benefit for the appearance drying) bluestained wood. and performance of wood in outdoor use. True outdoor testing is needed to clarify the implications. Bluestained lumber may be a good candidate for decking material. Property Tested Results Implications Permeability and Bluestained sapwood wets more Bluestained sapwood is more easily treated treatability with readily with water. The heartwood with wood preservatives and fire retardants. preservatives resistance to treatment is unchanged. Note that the green tint of many preservatives reduces the colour contrast between bluestained and non-bluestained wood. The combined benefits of bluestain-masking, increased treatability and improved checking appearance indicate that bluestained lumber heavy-to-sapwood is probably a good choice for treated decking products. Increased permeability may have implications for air or kiln drying—bluestained wood may dry faster. Glue joint integrity No difference between bluestained and No changes required for use of either non-bluestained wood in joint durability structural or non-structural adhesives with and strength. bluestained wood. Finishes for Best masking of bluestain for furniture Furniture manufacturers could use masking bluestain grade products is achieved with stains, combinations of these tints to reduce the toners or glazes containing blue, red or colour contrast between bluestained and non- charcoal tints. bluestained wood without making the final product too dark. Finishes for Clear finishes are best at enhancing or Some people find the bluestain visually enhancing bluestain highlighting the bluestain. appealing. Finish adhesion No difference between bluestained and No changes required in the use of stains, non-bluestained wood. toners and glazes. Test details Over 500 8’,10’ and 12’ pieces of lodgepole pine 2x4 ing quality was done using the block shear test by or 2x6 lumber were collected from 14 B.C. interior compression loading, in accordance with ASTM and sawmills for these tests. other standards. The evaluation of mechanical properties involved The finish tests were limited to furniture finishes that, clear wood tests, which are sensitive indicators of unlike paints, do not completely hide the wood’s any potential impact of bluestain on performance of natural appearance. A variety of stain, toner and lumber. Full-size lumber may contain knots, sloped glaze finishes were applied to the samples, alone grain and so forth, all of which are more critical and in combination. Finish adhesion was tested us- factors for mechanical properties outweighing any ing ASTM standard industry tape tests. Appearance small effect of bluestain. Toughness (also known as evaluations for the various finishes were subjective. impact bending strength), stiffness (bending modu- lus of elasticity - MOE), breaking strength (modulus of rupture - MOR), and the parallel-to-grain lateral resistance of the truss plate teeth in tension were all tested according to appropriate ASTM or CSA standards. There is no standard test for dimensional stability More Information and checking of lumber in service caused by re- Tony Byrne, Research Scientist peated wetting and drying. Forintek has developed Durability and Protection Group - Western Division and regularly uses its own accelerated wetting/drying Tel: (604) 222-5650 / Fax: (604) 222-5690 protocol and assessment procedure. Various mea- email@example.com sures of how far off “true” the lumber was (bow, crook, cup, twist), check length and check width Details on this work are available in several Forintek reports. For informa- were measured, and appearance of the checks was tion on acquiring Forintek reports, please consult our web site or phone our library in the Western Laboratory. visually assessed and assigned a rating. Permeability to liquid was tested in both simple soak- ing and pressure treatment. The wood preservative chromated copper arsenate (CCA) was used as a This document is available in Japanese Translation. tracer, since permeability characteristics are impor- tant to the wood treatment process. An additional benefit of CCA as a tracer is that it stops moving into the wood immediately upon completion of the soak or pressure process. Uptake and retention were measured for all samples. Before and after weights were also measured. The glue joint tests were conducted to determine performance for typical applications in both struc- tural and non-structural uses. To simulate a non- structural application such as furniture, panels were made using radio frequency-curable polyvinyl ac- etate (PVA) adhesive. For an example of a structural application such as glulam, pieces were joined using phenol resorcinol formaldehyde (PRF). The integrity of the glue joints was tested using the vacuum pres- sure delamination test, and assessment of bond- Forintek Canada Corp. acknowledges the assistance provided by the Province of British Columbia, through the Forestry Innovation Investment Program. Forintek Canada Corp., would like to thank its industry members, Natural Resources Canada (Canadian Forest Service), and the Provinces of British Columbia, Alberta, Saskatchewan, Quebec, New Brunswick, Nova Scotia, and Newfoundland and Labrador, for their guidance and financial support for this research.
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